In many snow removing machines provided with an auger, there is employed a technique in accordance with which the auger is varied in height in accordance with conditions of snow removal work. When the snow removing machine should travel, it can do so more efficiently with the lower end surface of the auger positioned higher. When, on the other hand, the snow removing machine should remove snow, it can do so more efficiently with the lower surface of the auger positioned lower. Further, in many cases, the height of the auger is adjusted in accordance with road surface irregularity or unevenness. Where the auger height is adjusted through manual input operation by a human operator, the input operation tends to be a great load on the human operator.
Auger-type snow removing machines, constructed to move the lower end surface of the auger in an upward/downward direction in order to reduce a load on a human operator, are known, for example, from Japanese Patent Post-Exam Publication No. SHO-61-30085 and Japanese Utility Model Laid-Open Publication Nos. SHO-63-194927 and SHO-64-31418.
FIG. 20 is a side view showing the conventional auger-type snow removing machine disclosed in SHO-61-30085. The auger-type snow removing machine 200 of FIG. 20 is a self-propelled vehicle, in which a vehicle body frame 204 having an engine 203 mounted thereon is vertically pivotably connected at its rear end portion to a running-device frame 202 having left and right running devices 201 mounted thereon. Further, in the disclosed auger-type snow removing machine 200, an auger housing 205 and blower case 206 are rollably connected to a front end portion of the vehicle body frame 204.
The left and right running devices 201 are in the form of left and right crawlers. The auger housing 205 houses an auger 207, and the blower case 206 houses a blower 208. The snow removing machine 200 can travel with output power of the engine 203 transmitted via a transmission device 209 to the running devices 201. Switching between forward and rearward running and between left and right turning of the running devices 201 can be effected by the human operator manipulating operation levers 211 etc. Snow can be removed by the output power of the engine 203 being transmitted via a belt transmission mechanism 213 to the auger 207 and blower 208.
Front portion of the vehicle body frame 204 can be moved in the upward/downward direction via an auger housing elevator mechanism 222 by the human operator pivoting an auger-housing-posture manipulating lever 221 in a forward/rearward direction, in response to which the auger housing 205 can be moved in the upward/downward direction.
Further, the auger housing 205 and blower case 206 can be rolled via a rolling drive mechanism 223 by the human operator pivoting the auger-housing-posture manipulating lever 221 in a leftward/rightward direction.
In general, when the snow removing machine 200 is to be turned in a desired direction, one of the running devices 201, which is located inwardly of the other as viewed in the turning direction, is slowed down. However, a coefficient of friction between a snow surface and the running devices 201 is smaller than a coefficient of friction between an ordinary road surface and the running devices 201. Furthermore, even when one of the running devices 201 (hereinafter “inner running device”) which is located inwardly of the other (hereinafter “outer running device”) as viewed in the turning direction is slowed down as the snow removing machine 200 is turned during low-speed travel, e.g. immediately before stoppage of the machine 200, there can be created only an extremely small difference in traveling speed between the inner running device 201 and the outer running device 201.
Particularly, the running devices 201, which are in the form of crawlers, present a great ground contact capability and great driving force inherent to the crawlers. If the speed difference between the left and right crawlers is small, the tractive force of the inner crawler 201 is not so great as compared to the tractive force of the outer crawler; namely, the speed difference between the inner and outer crawlers can not increase as required. Thus, it tends to be difficult to attain a desired turning radius when the human operator performs operation for switching from the straight travel to the turning travel, and further improvements must be made in order to allow the snow removing machine 200 to smoothly switch from the straight travel to the turning travel.